In the integrated wiring system, the transmission medium is different for different environments. The commonly used transmission media are twisted pair (also known as twisted pair), twisted pair symmetrical cable (referred to as symmetrical cable), coaxial cable and fiber optic cable (referred to as optical cable) 4 kinds. Today, I will introduce these four transmission materials in detail:
ZR Cable integrated wiring system
1. Twisted pair
At present, the diameter standards of twisted conductors are different internationally, and foreign manufacturers often use American Wire Gauge (AWG) as the standard for the diameter of cable conductors. Every third increment of the American Wire Gauge reduces the cross-sectional area of the conductor it represents by half, while the resistance value can be doubled.
2. Twisted pair symmetrical cable
When multiple pairs of twisted pairs form a cable structure, it becomes a symmetrical twisted pair cable. According to whether shielding measures are adopted in the cable structure, it can be divided into unshielded twisted pair symmetrical cable (UTP) and shielded twisted pair symmetrical cable. According to the different shielding layer materials, it can be divided into various models, such as FTP, STP and SFTP and other shielded twisted pair symmetrical cables.
UTP is an unshielded cable with no shielding layer structure. It has the characteristics of light weight, small size, good elasticity, convenient use and reasonable price, so it is widely used, even on links that transmit higher-speed data. However, its resistance to external electromagnetic interference is poor, and its equilibrium twist is easily damaged due to pulling and bending during installation. Therefore, it cannot meet the requirements of EMC (Electromagnetic Compatibility). External radiation, easy to leak, should not be used in the projects of important departments such as the party, government, military and finance.
STP (each pair of cores and cables are wrapped with aluminum foil, and copper braided), FTP (longitudinal aluminum foil) and SFTP (longitudinal aluminum foil, copper braided) paired pair symmetrical cables are shielded cables with shielding layers , has the characteristics of preventing external electromagnetic interference and external radiation, but they all have problems such as heavy weight, large volume, high price and difficult construction. In construction, complete shielding and correct grounding are required to ensure the characteristic effect. Therefore, when choosing whether to use shielded cables, it should be selected from a comprehensive consideration of security engineering construction, the nature of use of intelligent buildings and intelligent communities, the environment and future development.
3. Coaxial cable
Coaxial cables are generally not used in integrated wiring systems, and are mainly used in computer network systems. The coaxial cable used in the computer network system is divided into two types: baseband coaxial cable and broadband coaxial cable. The specific use is as follows.
(1) Baseband coaxial cable The baseband coaxial cable uses a copper metal braided mesh shield with a characteristic impedance of 50Ω, such as RG-8 and RG-11 thick coaxial cables and RG-58 thin coaxial cables. The outer diameter of the thick coaxial cable is about 13mm. The outer diameter of the thin coaxial cable is 6.4mm.
At present, the network of computer systems widely uses Ethernet, and its cable connection is divided into two types: thick cable interface and thin cable interface according to different interface standards. When the thick coaxial cable is installed on the network interface, it is not necessary to cut the coaxial cable, and the network access position of the computer can be flexibly adjusted according to the actual needs of the user, but the transceiver and the transceiver connecting cable (also known as the transceiver cable) must be installed on the network. or sending and receiving cables), therefore, the installation and construction are more difficult and the overall cost is higher. The thick coaxial cable interface method is generally used in relatively large local area networks, and its standard distance is long and its working reliability is high.
In the thin coaxial cable interface method, the cable must be cut off during installation, and the basic network connectors must be installed at both ends, and then connected to both ends of the T-type connector. Therefore, the installation and construction are simple and the project cost is low, but the capacity will be generated when there are too many connectors. The hidden danger of poor contact is the most common fault in the operation of Ethernet at present. Whether thick coaxial cable or thin coaxial cable is used in the network of the computer system, the following two points should be paid attention to:
a. When the network topology is bus type, and multiple computers are connected on a coaxial cable, due to a fault somewhere, it will directly affect the work of all computers on the entire cable, and will be helpful for diagnosis and elimination. failures are affected. For this reason, although this kind of network structure can be applied to occasions where computers are densely distributed, the number of connected computers should still be considered in the design, otherwise twisted pairs or optical cables should be used.
b. In order to keep the electrical characteristics of the coaxial cable unchanged, the cable shielding layer must be complete and well grounded. At the same time, terminators should be installed at both ends of the coaxial cable to weaken the signal reflection and ensure the quality of information transmission.
(2) Broadband coaxial cable Broadband coaxial cable is mainly used for the transmission of TV programs or broadband data. The shielding layer of the coaxial cable is made of aluminum foil stamping, and its characteristic impedance is 75Ω. Commonly used broadband coaxial cables are RG-59 Wait.
4. Optical fiber cable
The optical fibers (optical fibers for short) currently used in optical cables can be divided into different types according to the material composition used, the manufacturing method of the optical fiber, the transmission mode of the optical fiber (or the total transmission mode), the refractive index distribution on the optical fiber cross-section, and the working wavelength. The categories are introduced by the most commonly used operating wavelengths, transmission modes and fiber core diameters in the integrated wiring system.
(1) Divided by working wavelength
Short wavelength region (first window) 0.85μm (0.8μm-0.9μm); long wavelength region (second window) 1.30μm (1.25μm-1.35μm); long wavelength region (third window) 1.55μm (1.53μm- 1.58 μm).
(2) Divided by transmission mode
Multimode fiber (MMF) includes two types: gradual change type (also known as gradient type, gradual change type) and mutation type (also known as step type). The 0.85μm short wavelength region is a multimode fiber, and the 1.30μm long wavelength region is a multimode fiber, and there are also single mode fibers; ·Single mode fiber (SMF) is generally abrupt. In the 1.55μm long wavelength region, they are all single-mode fibers.
(3) According to the fiber core diameter, the classification is expressed by the fiber core diameter and the cladding diameter.
50μm/125μm (fiber core diameter/cladding diameter) multimode fiber with a slowly varying refractive index; 62.5μm/125μm reinforced multimode fiber with a slowly varying refractive index; 8.3μm/125μm abrupt refractive index single-mode fiber optical fiber.
At present, the optical fibers used in the integrated wiring system according to the working wavelength are 0.85μm and 1.30μm. Considering the core diameter of multimode fiber, it is recommended to use two types of fibers, 50μm/125μm or 62.5μm/125μm. In the case of higher requirements, 8.3μm/125μm mutant single-mode fiber can also be used, among which 62.5μm/125μm The slowly-deformed enhanced multimode fiber is used more. Because it has high optical coupling efficiency, large fiber core diameter, low requirements for fiber alignment during installation and construction, and less equipment, its transmission characteristics will not be too large when the cable is slightly bent or bent. changes, etc.
